1. Field of the Invention
The invention relates to flow-selector valves and particularly such valves that may be used in disposable sterile fluid lines, for example, lines used for extracorporeal blood processes.
2. Background
Hemofiltration, dialysis, hemodiafiltration, and other extracorporeal blood treatments may employ flow selector valves such as Y-valves, four-way valves, and other such devices for redirecting the flow of blood and other fluids such as replacement fluids. For example, the direction of the flow of blood through certain types of filters may be reversed repeatedly to prevent coagulation of blood in regions where the mean flow slows to very low rates. For example, where blood is circulated through tubular media in the context of a dialysis filter, it has been proposed that blood may coagulate on the surface of the inlet header leading to the progressive coagulation of blood. U.S. Pat. No. 5,605,630, proposes occasionally reversing the flow of blood through the filter. A four-way valve is proposed for changing over the flow direction.
In other references, the idea of reversing the flow of blood through a tubular media filter is discussed in connection with other issues. For example, in U.S. Pat. No. 5,894,011, the known technique of switching access lines in the patient to improve the flow through an occluded fistula is automated by the addition of a four-way valve on the patient-side blood circuit. In single-access systems in general, for example as described in U.S. Pat. No. 5,120,303, flow is conventionally reversed through the filter during each draw/return cycle. In the ""303 reference, the specification observes that the efficiency of filtration is increased due to the double-passing of the same blood through the filter; that is, each volume of drawn blood is filtered twice. Yet another reference, U.S. Pat. No. 6,189,388 B1, discusses reversing the flow direction of blood through the patient access occasionally in order to quantify an undesirable short-circuit effect that attends their long term use. Still another U.S. Pat. No. 6,177,049 B1 suggests reversing flow through the draw access before treatment while an observer is present to test the accesses for patency or to clear blockage in the accesses.
In copending commonly assigned application titled xe2x80x9cDevice And Method For Enhancing Performance Of Membranes And Filters,xe2x80x9d which is hereby incorporated by reference as if set forth in its entirety herein, a Y-shaped flow selector switch is described in connection with the selective direction of replacement fluid into the blood circuit of a hemofiltration system.
Referring to FIGS. 1A through 1E, a number of alternative designs for four-way valves have been developed for blood circuits. Referring to FIG. 1A, U.S. Pat. No. 5,894,011, discloses a valve that swaps the connections between pairs of lines 905 and 906 via a pair of rotatably connected disks 901 and 902, each of which supports one of the pairs of lines 905 and 906. A seal must be maintained between the disks 901 and 902 and between the respective lines. The device is intended to be operated manually.
Referring to FIG. 1B, another four-way valve, disclosed in U.S. Pat. No. 5,605,630, which has been proposed for use in blood lines, has a rotating wheel 910 with channels 911 and 912 defined between the wheel 910 and the inside of a housing 913. When the wheel is rotated, the channels 911 and 912 shift to join a different pair of lines. This device also has seals.
Referring to FIG. 1C, another arrangement is proposed in U.S. Pat. No. 6,177,049. This device has a rotating component 915 with channels 921 and 922 defined within it. As the rotating component 915 is rotated, the channels defined between pairs of lines 917 and 919 change from parallel lines joining one set of corresponding lines to U-shaped channels joining a different set.
Referring to FIGS. 1D1 and 1D2, a design, disclosed in U.S. Pat. No. 4,885,087, is very similar to that of FIG. 1B. This design has a rotator 925 that connects different pairs of lines depending on the position thereby defining two different sets of possible flow channels 926 and 929 or 927 and 931.
In all of the above designs, the valves are not hermetically sealed. Any seal can be compromised, particularly by microorganisms. Thus, each of the foregoing designs suffers from that drawback. Also, many are expensive and do not lend themselves to automation.
Referring to FIG. 1E, another type of four-way valve is formed by interconnecting two tubes 937 and 938 with crossover lines 935 and 936. This design is disclosed in U.S. Pat. No. 6,189,388 (Hereafter, xe2x80x9cU.S. Pat. No. ""388xe2x80x9d). Tube pinching actuators 941-944 are used to force fluid through different channels, depending on which actuators are closed. This device provides a hermetic seal and can be fairly inexpensive, but in a given configuration, significant no-flow areas are defined. These dead spaces can lead to the coagulation of blood, which is undesirable. Also, the interconnection of tubes in this does not lend itself to automated manufacturing.
The design of USP ""388 provides an important benefit for sterile fluid lines. Because it has no seals which seal the external environment from the portions that are wetted by sterile fluids, there is no danger of contamination by infiltrating microorganisms or other contaminants. Also, the narrow spaces that attend the presence of sealsxe2x80x94small gaps between movable parts and stationary partsxe2x80x94are places where fluid can stagnate, which can cause coagulation of some fluids or other adverse effects, depending on the fluid and application. The design of USP ""388, however, does have the serious deficiency of providing very long lengths of tubing in which no flow will occur at any given time while in use. This can lead to stagnation.
There exists in the prior art a need for flow directing valves that combine the features of potentially low cost so that they can be replaced as part of a sterile package, no tendency to create stagnation regions where there is no flow, and the capability of providing a hermetic seal to the environment.
Briefly, A flow diverting appliance has a flexible valve body to which a number of flow lines are connected. The valve body is deformed to create different flow paths within it. The valve body may be deformed, for example, by pinching it to define press-seals in an enclosed volume inside the valve body. The press seals divide the enclosed volume to form exclusive flow channels which allow communication between some flow lines and permit flow communication between other lines. The invention provides a way of making flow diverters part of a replaceable blood circuit which is fully hermetic and with no dead-end spaces which would allow blood to coagulate.
The valve body may be incorporated in a disposable fluid line for use in extracorporeal blood processing equipment. The valve body may be made integral with multiple flow lines and may define a Y-shaped flow selector, a four-way valve, or other possible configurations. When deformed by actuators, the valve body assumes one of multiple configurations, each defining one or more selectable flow passages. By deforming the valve body, fluid can be made to reverse flow direction or be directed along selected paths.
Portions of the valve body may be made from a flexible polymer such as polyvinylchloride (PVC). The operating temperature and gauge pressure impose constraints on the material thickness, shape, and other features. In a preferred embodiment of a four-way valve, a cylindrical section is ultrasonically sealed around a pair of tubes inserted at each open end forming a sealed bladder. In this embodiment, the material, for example, PVC, has a high degree of resilience and assumes a pillow shape even in the presence of a negative gauge pressure. This structure forms the valve body, which is pinched by anvils to form a seal in the center of the bladder. Two anvils are used. One pinches the bladder in one direction to form a pair of parallel channels uniting two pairs of the four lines and the other pinches it in a perpendicular direction to form a pair of U-shaped channels uniting two other pairs of the four lines.
In another embodiment of a four-way valve, an injection-molded cross of flexible material is connected to four lines. The actuator anvils pinch the cross at respective diagonal angles cutting it into respective sets of right-angle conduits to join the respective lines. In a Y-shaped flow diverter, three lines are inserted in a cylinder of ultrasonically weldable polymer and sealed to a bladder. To actuate this embodiment, anvils selectively cut off one of the lines by pinching the bladder.
In other embodiments, the bladder may be made thinner-walled and held open by means other than the strength and resilience of the material. For example, engagement devices may be provided on the outside of a bladder which are pulled apart by the actuator. Alternatively, in addition to anvils, the actuator may be provided with supports which squeeze or support parts of the valve body from the sides to keep it from collapsing.
In another aspect of the invention, where two anvils are used, the anvils are arranged on opposite sides of the valve body. One is urged by a spring and the other is urged by a solenoid. When the solenoid is activated, the solenoid-urged anvil pushes the spring-urged anvil back away from the valve so that only former deforms the valve body. When the solenoid is released, the spring-urged anvil pushes the solenoid-urged anvil back so that only the spring-urged anvil deforms the valve body. In this way, the device can be actuated with only one active actuator mechanism. Note that although the discussion contemplates a solenoid, the actuator could employ any suitable device, for example, a screw-driven linear actuator, a hydraulic or pneumatic actuator, or other compatible mechanism.
In all of the above embodiments, no significant dead spaces occur in the running lines, as distinguished from prior art valves. Also, the structure of the valve body lends itself to incorporation in fully premanufactured and sterilized fluid lines. In addition, the actuator mechanism is simple and requires few moving parts.
The avoidance of dead spaces requires that a bulk flow be such as to insure that all fluid in a region is moving. This can be insured by designing the flow regions in such a way as to insure that the length scale of the flow channel cross-section is not much smaller than any channel dead ends. That is, the channel length where no flow occurs should not be much greater than its diameter, including an inlet transition. This insures that momentum is transferred to the fluid in these areas to prevent stagnation of flow. This transfer can happen as a result of viscous diffusion of momentum or turbulent diffusion of momentum. If the flow is rapid enough or the diameters large enough (i.e., high Reynolds number), turbulent diffusion can reach multiple diameters into dead end channels. In medical applications, it is considered impractical to provide flow channels with a high degree of turbulent energy and so the design constraint is to insure that the dead end channels are no more than one or two diameters in length. Clearly this is not the case with USP ""388.
The invention will be described in connection with certain preferred embodiments, with reference to the following illustrative figures so that it may be more fully understood. With reference to the figures, it is stressed that the particulars shown are by way of example and for purposes of illustrative discussion of the preferred embodiments of the present invention only, and are presented in the cause of providing what is believed to be the most useful and readily understood description of the principles and conceptual aspects of the invention. In this regard, no attempt is made to show structural details of the invention in more detail than is necessary for a fundamental understanding of the invention, the description taken with the drawings making apparent to those skilled in the art how the several forms of the invention may be embodied in practice.